1. Field of the Invention
The present invention relates to a forming method of an alignment film for a liquid crystal display cell, which employs liquid crystals, for example, of smectic and nematic phases and effects display in response to a variation in orientation of their molecules.
2. Description of the Prior Art
An alignment contacts with molecules of a liquid crystal and serves to direct the arrangement of the liquid crystal molecules in a predetermined direction. For this purpose, a film has conventionally been utilized which is provided at its surface with a plurality of grooves arranged in a predetermined direction. Its particular manufacturing method is described in "SID International Symposium Digest of Technical Papers", P. 100 (1972). The groove can be made first by forming a substrate with an organic film at its surface and then by rubbing the surface of its film. The alignment film manufactured by the rubbing method has the drawback that its contact with a liquid crystal material for a long time causes a structure at its intersurface to be changed gradually with the result of irregularity in the orientation of the liquid crystal because the alignment film employs the organic film.
U.S. Pat. No. 3,834,792 of J. L. Jannig (Alignment film for a liquid crystal display cell) discloses a technique in which the alignment is formed by using an inorganic evaporation film instead of using the organic film. In this method, the substrate is so disposed in a vacuum evaporation container that its surface may be disposed at a low angle relative to an evaporation source to cause corpuscles flying downwardly from a predetermined oblique direction to be deposited on the surface of the substrate. The alignment film formed by the oblique vacuum evaporation method provides uniaxial anisotropy relative to the direction of the evaporation source and thus orients the liquid crystal molecules.
In the above-mentioned method, the evaporation source must be disposed in a very limited positional relation to the substrate in order to ensure a uniform orientation. Assuming, for example, that a distance from the evaporation source supposed to be a point to the substrate is 50 cm and an angle of evaporation for the oblique evaporation film is desired to be set in the tolerable range of 68 .+-. 2.degree. in the oblique evaporation method, the substrate must be below about 40 mm in diameter in the direction of evaporation source. If the substrate is above 40 mm in diameter, then the angle of evaporation amounts at both its ends to more than 4.degree.. This results in formation of no uniform orientation and in defective display.
The alignment film formed by the oblique vacuum evaporation method provides uniaxial anisotropy only in the direction of evaporation source, so that it does not exhibit sufficiently great orientation controlling power for the liquid crystal. For, for example, a liquid crystal with a shiff base ##STR1## exhibiting an excellent orientation at its interface, the film exhibits good controlling ability, but for a liquid crystal with an azoxy base ##STR2## having a great response when used as a display cell, it exhibits no orientation controlling characteristics. In the chemical expression, R and R' show an alkyl group.